1. Field of the Invention
The present invention relates to a scanning probe microscope and specimen observation method and semiconductor device manufacturing method using said scanning probe microscope.
2. Description of the Related Art
An example of known technology for measuring minute three-dimensional shapes is provided by an SPM (scanning probe microscope). This is a widely employed technique whereby minute three-dimensional shapes of the atomic order can be measured, by scanning a sample whilst maintaining the contacting force at an extremely small value while controlling a probe with a sharp tip. Various improvements have previously been made directed at the problem, characteristic of scanning probe microscopes, that it is difficult to raise the speed of physical scanning of the sample.
For example, in Laid-open Japanese Patent Publication Number H. 10-142240 and Laid-open Japanese Patent Publication Number 2000-162115, a technique is disclosed for correcting shape data from both a probe flexure signal and a sample drive signal, in order to obtain both improved speed and better resolution. Also, in Laid-open Japanese Patent Publication Number H. 6-74754, a technique is disclosed of bringing up the probe at high speed whilst vibrating the probe until it is close to the sample, from a location that separated therefrom by about 5 micrometers, by utilizing a construction such that the probe amplitude can be reduced by acoustic interaction when the sample is approached, in order to bring the probe up close to the sample at high speed. However, the above technique is subject to the problem that it can only be employed in a scanning probe microscope of a construction in which the probe is vibrated and to the problem that a further separate sensor must be provided in order to bring the probe up at high speed to a distance of a few micrometers, since proximity cannot be sensed unless the probe is no more than a few micrometers from the sample.
Currently, also, dimension control using a CD-SEM (distance-measurement SEM) is performed in the process of forming a fine pattern on an LSI, but the following restrictions are encountered as the fineness of the pattern is increased. (1) Problem of measurement accuracy: the gate width of a 90-nm node LSI, which is expected to become the most common type in 2003, is 80 nm; assuming that the allowed variability is 10% and that the measurement accuracy is 20% thereof, the required measurement accuracy is 1.6 nm. (2) Demand for profile measurement: the requirement for APC (Advanced Process Control) in order to achieve high-accuracy control of line width is increased, but, in order to achieve this, a technique for measurement of cross-sectional shape, whereby, in addition to pattern line width, electrical characteristics are greatly influenced, becomes necessary. (3) Problem of the subject of measurement: requirement for measurement of materials of low ability to withstand cathode rays, such as DUV (deep ultraviolet) resists, low-k (low permittivity) film materials is increasing. A similar requirement i.e. necessity of the same degree of measurement accuracy and for profile measurement for measurement of resist patterns for master production is anticipated in respect of measurement of the pits of next-generation high-density optical discs.
The above problems cannot be solved by current CD-SEMs. Scanning probe microscopy is considered to be promising in this connection. What is required is a scanning probe microscope whereby, in addition to the improvement in speed of probe approach described above, there is little damage to soft and brittle materials and information regarding the material quality of the surface can be obtained.
In this connection, Laid-open Japanese Patent Publication Number H. 11-352135 discloses a method of reducing damage to soft and brittle materials and to the probe by scanning whilst the probe is cyclically brought up against the sample whilst the sample, or the probe, is vibrated with a fixed amplitude. In addition, Laid-open Japanese Patent Publication Number 2001-33373 discloses a scanning method wherein height measurement is performed with the servo of the probe activated only at separated measurement points, the probe being moved towards the next measurement point in a raised condition. With this method, contact pressure is even smaller and damage to the soft and brittle material and to the probe is small. A further advantage is that faithful measurement of the shape of steps can be performed, since the probe is not dragged over the surface. However, although, when measurement of a pattern such as that of a resist is to be performed, it is desirable to measure the shape of the pattern bottom and, in addition, to obtain by measurement information as to whether any of the resist is left at the bottom, this method was not able to meet these requirements. Also, it is necessary to raise the resonance frequency of the probe and reduce the inertia of the probe in order to achieve higher speeds, and, with this in view, it was necessary to make the cantilever section at the tip of the probe small. However, with the conventional optical lever system, an area of the order of 50 micrometers is necessary in order to ensure and adjust a reflective surface for the laser, so there were limitations to the extent to which improvement in speed could be achieved.
As described above, with the prior art, there were problems concerning increasing the speed of approach of the probe to the sample in order to improve measurement throughput.